Transfluthrin eave-positioned targeted insecticide (EPTI) reduces human landing rate (HLR) of pyrethroid resistant and susceptible malaria vectors in a semi-field simulated peridomestic space

Abstract

Background Volatile pyrethroids (VPs) are proven to reduce human–vector contact for mosquito vectors. With increasing resistance to pyrethroids in mosquitoes, the efficacy of VPs, such as transfluthrin, may be compromised. Therefore, experiments were conducted to determine if the efficacy of transfluthrin eave-positioned targeted insecticide (EPTI) depends on the resistance status of malaria vectors. Methods Ribbons treated with 5.25 g transfluthrin or untreated controls were used around the eaves of an experimental hut as EPTI inside a semi-field system. Mosquito strains with different levels of pyrethroid resistance were released simultaneously, recaptured by means of human landing catches (HLCs) and monitored for 24-h mortality. Technical-grade (TG) transfluthrin was used, followed by emulsifiable concentrate (EC) transfluthrin and additional mosquito strains. Generalized linear mixed models with binomial distribution were used to determine the impact of transfluthrin and mosquito strain on mosquito landing rates and 24-h mortality. Results EPTI treated with 5.25 g of either TG or EC transfluthrin significantly reduced HLR of all susceptible and resistant Anopheles mosquitoes (Odds Ratio (OR) ranging from 0.14 (95% Confidence Interval (CI) [0.11–0.17], P < 0.001) to 0.57, (CI [0.42–0.78] P < 0.001). Both TG and EC EPTI had less impact on landing for the resistant Anopheles arabiensis (Mbita strain) compared to the susceptible Anopheles gambiae (Ifakara strain) (OR 1.50 [95% CI 1.18–1.91] P < 0.001) and (OR 1.67 [95% CI 1.29–2.17] P < 0.001), respectively. The EC EPTI also had less impact on the resistant An. arabiensis (Kingani strain) (OR 2.29 [95% CI 1.78–2.94] P < 0.001) compared to the control however the TG EPTI was equally effective against the resistant Kingani strain and susceptible Ifakara strain (OR 1.03 [95% CI 0.82–1.32] P = 0.75). Finally the EC EPTI was equally effective against the susceptible An. gambiae (Kisumu strain) and the resistant An. gambiae (Kisumu-kdr strain) (OR 0.98 [95% CI 0.74–1.30] P = 0.90). Conclusions Transfluthrin-treated EPTI could be useful in areas with pyrethroid-resistant mosquitoes, but it remains unclear whether stronger resistance to pyrethroids will undermine the efficacy of transfluthrin. At this dosage, transfluthrin EPTI cannot be used to kill exposed mosquitoes.

Human landing catches provide a useful measure of protective efficacy for the evaluation of volatile pyrethroid spatial repellents

“…A short exposure time was used in the experiments to mimic real life, as mosquitoes are likely to be exposed to a treatment for only a short period of time before their behavioural responses are elicited [41]. There was no interaction between treatment and species, indicating that transfluthrin used at the concentrations in this experiment induced protection against all the mosquito species tested, regardless of their resistance mechanism, in agreement with previous work [27]. The calculated PE was similar between the landing and biting experiments.…”

“…gambiae Kisumu strain (KDR), which is a pyrethroid-resistant mosquito. However, this resistance does not greatly impact landing behaviour in the setting used here [27], thus, this lack of difference could have been due to chance. Further evaluation of landing versus biting methods are ongoing, using formulated products in semi-field and experimental hut experiments, to see if they confirm the findings of this study.…”

“…A concentration series of EC transfluthrin (Bayothrin EC; Bayer, Monheim am Rhein, Germany) was prepared. Eave-positioned targeted insecticide (EPTI) emanators comprising 4 m × 0.1 m strips of hessian treated with 5 g, 10 g, 15 g, or 20 g of transfluthrin [27] were used for the experiments with Anopheles. For Aedes mosquitoes, freestanding transfluthrin passive emanators (FTPEs) [28] comprising 5 m × 0.1 m hessian strips treated with the same four doses of transfluthrin were used.…”

Influence of testing modality on bioefficacy for the evaluation of Interceptor® G2 mosquito nets to combat malaria mosquitoes in Tanzania

“…For each test, 60 nulliparous, sugar-starved, 5–8-day-old, laboratory-reared female mosquitoes were released per chamber with 15 mosquitoes per strain. Morphologically identical Anopheles mosquito species were marked with non-toxic fluorescent dye to distinguish them [ 20 ].…”

Insecticide-treated eave ribbons for malaria vector control in low-income communities

“…Hence eave ribbons have potential in managing insecticide resistance Masalu et al [ 45 ] 10 Predicting the impact of outdoor vector control interventions on malaria transmission intensity from semi-field studies Statistical modelling of semi field eave ribbons data from Tanzania and Kenya Laboratory-reared Anopheles arabiensis 41–96% Transfluthrin treated eave ribbons provide both personal and community protection. Denz et al [ 49 ] 11 Transfluthrin Eave-Positioned Targeted Insecticide (EPTI) Reduces Human Landing Rate of Pyrethroid Resistant and Susceptible Malaria Vectors in a Semi Field Simulated Peri-domestic Space Eave ribbons were treated following the procedures described by Mmbando et al [ 37 ] Laboratory-reared Anopheles arabiensis 80% 68% Transfluthrin treated eave ribbons have potential tackle the challenges of insecticide resistance in malaria vectors Tambwe et al [ 56 ] 12 Evaluating putative repellent ‘push’ and attractive ‘pull’ components for manipulating the odour orientation of host-seeking malaria vectors in the peri-domestic space Hessian strip [21 m × 0.05 cm] impregnated with 10 ml technical grade transfluthrin prepared in soapy water; the strips suspended overnight indoors to dry Tests were done in large semi-field cage Laboratory-reared Anopheles arabiensis Not assessed 94% Transfluthrin treated hessian fabric strips around eave gaps provide significant protection from mosquito bites in the peri-domestic spaces. Njoroge et al [ 57 ] The table focuses primarily on hessian-based eave ribbons and excludes other eave-based technologies …”